This invention relates to turbocharger control systems.
It is known that increasing the pressure of the air supplied to an internal combustion engine will increase the horsepower output, and various types of supercharging and turbocharging arrangements have previously been proposed to accomplish this purpose for internal combustion engines.
However, there are a number of factors which go into the optimum operation of a turbocharger or a supercharger. For example, when a turbocharger is operated by the hot exhaust gases from an engine, the back pressure on the engine is increased, and the efficiency of the engine is thereby reduced somewhat as a result of this increased back pressure. In addition, the compressor of a turbocharger must not be overdriven. More specifically, above a certain rate of rotation, with the diffuser vanes in a predetermined orientation or configuration, if the compressor speed is not in keeping with the appropriate mass flow rate for that given compressor speed and configuration or geometry the compressor will reach an undesired condition in which cavitation, or "surge" may occur. Under these conditions the compressor may suffer mechanical damage. This undesired phenomenon occurs at a driving speed which is only slightly above the optimum operating point of the compressor.
Up to the present time, although superchargers and turbochargers have been employed, they have generally not been operated at the optimum operating points for highest overall engine efficiency. Instead the superchargers have generally either been operated at a relatively low efficiency region where only a portion of the potential increase in horsepower has been realized, or at such a high level that intermittent cavitation or other failure of the supercharger to supply additional air to the intake manifold occurs.
In other prior systems using what is known as "waste-gate controls", a significant portion of the engine exhaust gases have been selectively diverted to the atmosphere to control the turbocharger rotational speed. Such controls waste a portion of the available energy which could otherwise be utilized for useful purposes. Accordingly, the very significant potential of turbochargers, which can increase engine power on the order of sixty (60%) percent when optimally employed, has generally not been realized.
In one prior art device disclosed in U.S. Pat. No. 3,173,242 issued to B. G. Erickson entitled "AIR-FUEL RATIO CONTROLS FOR ENGINES", the use of a conventional turbocharger having a turbine driven by engine exhaust gases which in turn drives a compressor which supplies compressed air to the inlet manifold is taught. This particular device teaches the use of an intercooler to prevent air temperature variations from causing air pressure fluctuations at the inlet. More particularly, this device provides a control system for matching the air provided by the compressor to the fuel actually delivered to provide an optimum mixture ratio. The amount of air supplied by the compressor is determined by the amount of exhaust provided to the turbine or by-passed by the turbine by a control valve.
This device works well for its intended purpose, a constant speed engine as determined by a fuel controlling speed governor that, due to its turbocharger control system, may respond quickly to changes in load. The control system is limited, however, to an optimum air-fuel mixture at one design speed of the engine. Since the optimum mixture changes with changes in engine speed in a non-linear manner, the control system would be ineffective at maintaining optimum operating conditions throughout a range of engine speeds or in excessive demand, "Jam", conditions. Further, no provision is made for preventing cavitation or stall conditions.
Another prior art device disclosed in U.S. Pat. No. 3,570,240 issued to J. Melchior entitled "SUPERCHARGING APPARATUS FOR DIESEL AND MULTIFUEL ENGINES" teaches the adaptation of a turbocharger to operate as a combustion chamber for use as an auxiliary power supply and for providing pressurized and heated air to the intake manifold for ease of starting a diesel engine. Included in this device is a control system for augmenting the exhaust gases with fuel in the turbine to maintain a constant speed of rotation of the compressor and turbine sections of the turbocharger.
This device provides the necessary pressure for start-up and high-load, low-speed demands of the engine. There is no disclosure in this patent relative to optimum performance over a range of engine speeds.
No apparatus was known prior to the present invention for providing a control system that would cause an optimal pressure of air to be supplied to an intake manifold for all engine speeds and load conditions. Further, no apparatus was known for providing a limited minimum turbocharger performance that is selctively limited to low engine speed (idle) conditions and which included cavitation and stall preventing controls.
A principal object of the present invention is, therefore, to provide a control system for the operation of a turbocharger whereby the diesel engine and turbocharger combination is efficiently operated at close to the maximum power output capability throughout the full power operating range of engine speeds, but safely below the "cavitation" or "stall" region of the compressor, whereby reliable high efficiency and high power operation is achieved. A subordinate object of the present invention is to accomplish the foregoing with a simple and reliable electronic circuit implementation.